Plural beam electron gun for a color picture tube with different-sized control grid apertures

ABSTRACT

In a color picture tube having plural beams emitted from a cathode structure to pass through respective apertures of a control grid structure for intensity modulation and being focused to impinge on respective color phosphors, the relationship of beam currents required for good white balance is achieved by giving a relatively large area to the control grid aperture corresponding to the beam, particularly the green beam, which is to have a relatively high beam current. Preferably, the grid aperture of large area is divided into parts so as to achieve the necessary increased beam current without a corresponding change in the cutoff voltage.

Unite States Patent inventors Susumu Yoshida;

Akio Ohgoshi, Tokyo; Senri Miyaoka,

Kanagawa-ken, Japan App]. No. 760,647

Filed Sept. 18, 1968 Patented Mar. 23, 1971 Assignee Sony Corporation Tokyo, Japan Priority Sept. 20, 1967 Japan 42/60133 and 42/60136 PLURAL BEAM ELECTRON GUN FOR A COLOR PICTURE TUBE WITH DIFFERENT-SIZED CONTROL GRID APERTURES 7 Claims, 13 Drawing Figs.

U.S. Cl 313/70, 313/92 Int. Cl H01j 29/50,

H01 j 31/20 Field of Search 313/92 (B), 69, 70 (C) [56] References Cited UNITED STATES PATENTS 2,726,347 12/1955 Benway 3 l3/7OC 2,825,845 3/1958 Jonker et al. 3 l3/70CX 2,825,847 3/1958 DeGier 3 l3/70CX 2,891,183 6/1959 Barnett 313/69 3,016,471 1/1962 Drake et al. 313/82 2,104,566 1/1938 Maloff 313/82X 2,111,940 3/1938 Schlesinger 313/82 3,448,316 6/1969 Yoshida et a1. 313/70CX 3,462,638 8/1969 Tetsuo et a1. 313/70CX Primary Examiner- Robert Segal Att0rneys-Albert C. Johnston, Robert E. lsner, Lewis H.

Eslinger and Alvin Sinderbrand ABSTRACT: In a color picture tube having plural beams emitted from a cathode structure to pass through respective apertures of a control grid structure for intensity modulation and being focused to impinge on respective color phosphors, the relationship of beam currents required for good white balance is achieved by giving a relatively large area to the control grid aperture corresponding to the beam, particularly the green beam, which is to have a relatively high beam current. Preferably, the grid aperture of large area is divided into parts so as to achieve the necessary increased beam current without a corresponding change in the cutoff voltage.

FLUPIAL BEAM ELECTRON GUN FOR A COLOR IPHQTKJRE TUBE WITH DIFFERENT-SIZED CONTRGL GRID APEIRTURES This invention relates generally to color picture tubes in which a plurality of intensity modulated electron beams are made to impinge on respective color phosphors on a screen scanned by the beams.

in color picture tubes, as above, three electron beams are made to impinge on respective phosphors which, when thus bombarded, emit red, green and blue light, respectively, with intensities that are dependent upon the beam currents. When these three colors are present in predetermined relative intensities, the eye at a distance perceives the combination as white, that is, a good white balance is obtained. However, when the predetermined relative intensities are not present, the dominant colors appear and create the chromatic components of the picture. Even though green sulfide phosphors have a higher luminance efficiency, that is, have a greater luminance intensity in relation to the current density of the beam impinging thereon, than do the red and blue sulfide phosphors, this is not sufficient to provide the predetermined relative intensities of the red, green and blue light required for a good white balance if the beam currents are the same. Thus, a good white balance of the picture requires that the beam current of the green beam be substantially greater than the currents of the red and blue beams.

Accordingly, it is an object of this invention to provide a color picture tube with an electron gun structure for directing the red, green and blue beams against the respective phosphors, and by which the beam current of the green beam may be relatively increased to provide a good white balance of the picture.

Another object is to provide an electron gun structure by which the desired high beam current of the green beam is obtained without correspondingly changing the cutoff voltage for that beam.

Still another object is to obtain the aforementioned relatively high current of the green beam without a corresponding change of its cutoff voltage while insuring that the three electron beams impinge on the respective phosphors at spots of substantially the same area.

In accordance with an aspect of this invention, the relationship of beam currents required for good white balance of the picture is achieved by giving a relatively large open area to the control grid aperture corresponding to the green beam, and preferably such aperture of large area is divided into two or more parts so as to relatively increase the current of the green beam without a corresponding change in its cutoff voltage.

Further, it is a feature of this invention to provide the foregoing in a color picture tube of the type in which the three electron beams are all focused on the screen by a common main electron lens and the beams are made to cross each other at the optical center of such main lens by means of an axially aligned auxiliary lens, with the green beam being generated centrally between the red and blue beams so as to pass through the center of the auxiliary lens while the red and blue beams pass through peripheral portions of the latter and hence are subjected to some spherical errors. Thus, although the green beam is generated with a larger cross section than the red and blue beams by reason of the large area grid aperture provided according to this invention, the mentioned spherical errors introduced by the auxiliary lens cause the spots at which the red and blue beams land or impinge on the screen to be of substantially the same area as the landing spot of the green beam.

The above, and other objects, features and advantages of this invention, will be apparent in the following detailed description of illustrative embodiments which is to be read in connection with the accompanying drawings, wherein:

H6. 1 is a schematic, axial sectional view of a color picture tube of a type to which this invention may be advantageously applied;

FIG. 2 is a graph showing the relationship of luminance to beam current density for the several phosphors employed on the screen of the tube shown on FIG. 1;

FIG. 3 is an enlarged, fragmentary sectional view of the cathode and control grid structures of the tube shown on HO. 1 when constructed according to a first embodiment of this invention;

FIG. 4 is a detail elevational .view of the control grid structure of FIG. 3 when viewed from the side thereof facing away from the cathode structure;

FIG. 5 is a graph showing the relationship of control grid voltage to anode current for the several beams of the tube embodying this invention;

FIGS. 6 and 7 are views similar to FIGS. 3 and 4, respectively, but illustrating another embodiment of the invention;

FIGS. 8 and 9 are views similar to FIGS. 4 and 7, respectively, but illustrating additional embodiments of the invention; and

FIGS. 10 to 13 are enlarged, detail elevational views showing further modifications of grid apertures as provided according to the invention.

Referring to the drawings in detail, and initially to FIG. 1 thereof, it will be seen that a single-gun, plural-beam color picture tube 10-of the type to which this invention may be advantageously applied may comprise a glass envelope (not shown) having a neck and a cone extending from the neck to a color screen S provided with arrays or sets of color phosphors S 5,; and S and with an ape'rtured beam selecting grid or shadow mask G Disposed within the neck is a single electron gun including a cathode structure K having three beamemitting surfaces disposed substantially perpendicular to the axis of the electron gun. In the embodiment shown, the beamemitting surfaces are arranged in a straight line so that the respective beams B B and B, emitted therefrom are directed in a substantially horizontal plane containing the axis of the gun, with the central beam B being coincident with such axis. A first grid structure G, isspaced from the beamemitting surfaces of cathodes K K and K and has apertures g g and g,,, formed therein in alignment with the respective cathode beam-emitting surfaces. A common grid G, is spaced from the first grid structure G, and has apertures g g and g formed therein in alignment with the respective apertures of the first grid structure 6,. Successively arranged in the axial direction away from the common grid G, are openended, tubular grids or electrodes G,,, G, and 6,, respectively, and cathode structure K, grids G, and G and electrodes 0,, G, and G are maintained in the depicted assembled positions thereof, by suitable, nonillustrated support means of an insulating material.

For operation of the electron gun of FIG. I, appropriate voltages are applied to grids G, and G and to electrodes G;,, G, and 0,. Thus, for example, a voltage of 0 to minus 400v. is applied to grid structure 6,, a voltage of 0 to 500v. is applied to grid 6,, a voltage of 13 to 20KV is applied to electrodes G, and G and a voltage of 0 to 400v. is applied to electrode G, with all of these voltages being based upon the cathode voltage as a reference. As a result, the voltage distributions between the respective electrodes and cathodes, and the respective lengths and diameters thereof, may be substantially identical with those of a unipotential-single beam-type electron gun which is constituted by a single cathode and first and second, single-apertured grids.

With the applied voltage distribution as described hereinabove, an electronlens field will be established between grid G and the electrode G to form a relatively weak auxiliary lens L as indicated in dashed lines, and an electron lens field will be established around the axis of the electrode 0,, by the electrodes 0,, G, and G to form a main focusing lens L, again as indicated in dashed lines. In a typical use of electron gun A, bias voltage of m, tlv., 360m, ZOKV, 206v and 20v. may be applied respectively to cathode structure K, first and second grids G, and G and electrodes G G, and G Further included in the electron gun of FIG. 1 are electron beam convergence deflecting means F which comprise shielding plates P and P disposed in the depicted spaced, relationship at opposite sides of the gun axis, and axially extending, deflector plates Q and O which are disposed, as shown, in outwardly spaced, opposed relationship to shielding plates P and P, respectively. Although depicted as substantially straight, it is to be understood that the deflector plates Q and may, alternatively, be somewhat curved or outwardly bowed, as is well known in the art.

The shielding plates P and P are equally charged and disposed so that the central electron beam B will pass substantially undeflected between the shielding plates P and P, while the deflector plates Q and Q have negative charges with respect to the plates P and P so that electron beams B and B will be convergently deflected, as shown, by the respective passages thereof between the plates P and Q and the plates P and 0. More specifically, a voltage V which is equal to the voltage applied to the electrode G may be applied to both shielding plates P and P, and a voltage V which is some 200 to 300v. lower than the voltage V,,, is applied to the respective deflector plates Q and Q to result in the respective shielding plates P and p being at the same potential, and to result in the application of a deflecting voltage difference or convergence deflecting voltages between plates P and Q and plates P and O, and it is, of course, this convergence deflecting voltage which will impart the requisite convergant deflection to electron beams B and E 0n operation, the electron beams B B and 8,, which emanate from the beam emitting surfaces of cathode structure K will pass through the respective grid apertures g g and g,,,, to be intensity modulated with what may be termed the red, green and blue intensity modulation signals applied between the cathode structure and the first grid structure 6,. The respective electron beams will then pass through the relatively weak common auxiliary lens L to cross each other at the optical center of the main lens L and to emerge from the latter with beams B and B diverging from bearn B Thereafter, the central electron beam B will pass substantially undeflected between shielding plates P and P since the latter are at the same potential. Passage of the electron beam B between the plates P and Q will, however, result in the convergent deflections thereof as a result of the convergence deflecting voltage applied therebetween, and the system of FIG. 1 is so arranged that the electron beams B B G and 8,, will desirably converge or cross each other at a common spot centered in an aperture between adjacent grid wires g of the beam selecting grid or mask G so as to diverge therefrom to strike the respective color phosphors of a corresponding array or set thereof on screen 8. More specifically, it may be noted that the color phosphor screen S is composed of a large plurality of sets or arrays of vertically extending red, green and blue phosphor stripes or dots S 8 and S with each of the arrays or sets of color phosphors forming a color picture element as in a chromatron-type color picture tube. Thus, it will be understood that the common spot of beam convergence corresponds to one of the thusly formed color picture elements.

The voltage V may also be applied to the lens electrodes G and G and to the screen S as an anode voltage in conventional manner through a nonillustrated graphite layer which is provided on the inner surface of the cone portion of the tube envelope. The grid wires of screen grid G, may have a post focussing voltage ranging, for example, from 6 to 7 KV, applied thereto. Thus, to summarize the operation of the depicted color picture tube of FIG. 1, electron beams B B and E will be converged at screen grid G and will diverge therefrom in such manner that electron beam B will strike the green phosphor S and electron beam 8,; will strike the red phosphor S of the array or set corresponding to the grid aperture at which the beams converge. Electron beam scanning of the face of the color phosphor screen is effected by horizontal and vertical deflection yoke means indicated in broken lines at 20 and which receives horizontal and vertical sweep signals whereby a color picture will be provided on the color screen. Since, with this arrangement, the electron beams are each passed, for focusing through the center of the main lens L of the electron gun A, the beam spots formed by impingement of the beams on the color phosphor screen 5 will be substantially free from the effects of coma and/or astigmatism of the main lens, whereby improved color picture resolution will be provided.

As shown generally on FIG l and in detail on FIGS. 3 and 4, the cathode structure K may include a unitary cathode member having all three beam emitting surfaces K K and K provided thereon, and the first grid structure G, associated therewith may include individual grid members G G and G provided with the respective apertures g g and G therein. In such case, the three color video signal voltages E,,, E and E,, for intensity modulating the beams B B and B are applied between cathode K and grid members G G and G respectively.

If it is assumed that the color phosphors S S and S, have the same luminance characteristics in relation to the current densities of the beams B B and B impinging thereon, it is necessary, in order to obtain a good white balance, that the three color video signal voltages for determining the beam current densities have the following relationships:

Even though, as shown in FIG. 2, the green sulfide phosphor has a higher efficiency, that is, a greater luminance in relation to the current density of the beam impinging thereon, than do the red and blue sulfide phosphors, it is still necessary to relatively increase the green signal voltage on the green electron beam current in order to obtain a picture with good white balance. In accordance with the present invention, as shown on FIGS. 3 and 4, the grid aperture g for passage of the green beam B is provided with a relatively large diameter D, so that the current and cutoff voltage of that portion of the electron gun for producing beam B are substantially larger than the current and cutoff voltages of the portions of the gun for producing the other beams B and B Therefore, the relatively large green video signal voltage E can be applied between cathode K and grid member G and the relatively large current of the green beam B necessary for obtaining a good white balance is achieved.

FIG. 5 illustrates the characteristics of the grid voltages E E and E,, to the anode currents I,;, I and I respectively, for the portions of the electron gun according to this invention which generate the beams B B and B respectively.

Although the embodiment shown on FIGS. 3 and 4, employs a one-piece or unitary cathode K in association with the individual first grid members G 6, and G it will be apparent that the invention may be similarly embodied in a color picture tube having such individual grid members associated with respective individual cathode members bearing the emitting surfaces K K and K or such individual cathode members K K and K may be associated with a unitary first grid member G, provided with all of the apertures g g and 811;, as shown on FIGS. 6 and 7.

In each of the above-described embodiments of the invention, the portion of the electron gun producing green beam 58 has a cutoff voltage different from the cutoff voltage of the portions producing the other beams B and B so that the same video output circuit cannot be used for driving the three gun portions. However, it has been found that the area of the aperture in the first grid structure for passage of the green beam B can be made relatively large to increase the green beam current, without correspondingly increasing the cutoff voltage of the portion of the gun generating the green beam by dividing the grid aperture for the green beam into two or more parts having the necessary large aggregate area.

For example, as shown on FIGS. 8 and 9, which correspond to the arrangements of FIGS. 4 and 7, respectively, a portion 21 of the grid member G or of the grid G, may diametrically span or bridge the aperture g therein to divide such aperture into parts 22a and 22b having an aggregate area which is large enough to provide the current of the green beam B necessary for good while balance. FIGS. 10, ll, 12 and 13 respectively illustrate at 21a, 21b, 21c and 21d other arrangements of bridging or spanning portions of the grid structure by which the large aperture g for the green beam can be divided into several parts to ensure that all beams will have the same or similar cutoff characteristics.

With the arrangements according to this invention shown on FIGS. 813, the large green beam current for good white balance can be obtained with a green video signal voltage that is substantially the same as the blue and red video signal voltages so as to permit substantial simplification of the circuits for driving the electron gun.

in the drawings, the grid apertures g and glB for the red and blue beams have been shown to be of the same size, however, since the luminance efficiencies of the red and blue phosphors may also differ from each other, as shown on FIG. 2, it may also be convenient and desirable to provide such apertures g and g with different areas, and hence to provide different beam currents to compensate for the different luminance efficiencies of the respective phosphors.

In the foregoing, the invention has been described as applied to a single-gun, plural-beam, color picture tube of the type shown on FIG. 1, that is, one in which the relatively weak lens L causes the beams B B and 3,; to cross each other at the optical center of main focusing lens L, but the invention is not limited in its application to color picture tubes of that particular type. However, in the color picture tube of the type described above with reference to FIG. 1, it is preferred that the relatively large grid aperture g provided according to this invention for the green beam B be given the central location, as shown. By reason of the relatively large area of aperture g the cross section of beam B is increased as is the area of the spot at which such beam impinges on screen S after focusing by lens L. On the other hand, the beams B and 3;; pass through peripheral portions of the auxiliary lens L so that the latter, although weak, introduces a slight spherical error in beams B and B to increase the areas of the spots at which such beams impinge on screen S. Thus, although beams B and B are generated with smaller cross sections than the beam E the central arrangement of the latter results in the three beams impinging on screen S at spots of substantially the same size.

Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the appended claims.

We claim:

1. In a color picture tube having a screen with different color phosphors thereon in a repetitious pattern to be made luminescent by the impingement thereagainst of respective intensity moldulated electron beams, and in which the phosphors of one color need to be excited by a beam current substantially larger than the beam currents for the other phosphors in order to obtain a good white balance; the combination of means for generating said electron beams including cathode means having emitting surfaces for the respective beams, and control grid means having portions thereof that are substantially equidistant from said emitting surfaces and apertures in said portions aligned with said emitting surfaces for the passage of the respective beams, the one of said apertures for the passage of the beam corresponding to the phosphors of said one color being of substantially larger open area than the other apertures to provide said substantially larger beam current when a corresponding larger video signal voltage is applied between the respective cathode and control grid means, and said one aperture being divided into parts by said grid means so that said larger open area is constituted by the aggregate area of said parts, whereb to provide said lar er beam current without a corresponding ifference between e respective cutoff voltages for said beams.

2. A color picture tube according to claim 1, in which said different color phosphors are red, green and blue, respectively, and the phosphors of said one color are the green phosphors.

3. A color picture tube according to claim 2, further comprising a main electron lens means to focus all of said beams on said screen and an auxiliary electron lens means to cause said beams to cross each other at the effective optical center of said main lens means, and in which the emitting surface and grid aperture for the beam corresponding to the green phosphors are located on the optical axis of said auxiliary and main lens means centrally between the emitting surfaces and grid apertures for the other beams so that the latter pass through peripheral portions of said auxiliary lens means and are subject to spherical errors thereby, whereby to ensure that the landing spots of all of said beams on the respective phosphors are substantially of the same area.

4. A color picture tube according to claim 1, in which said control grid means includes a unitary grid member having all of said apertures therein.

5. A color picture tube according to claim 4, in which said cathode means includes individual cathode members each having a respective one of said emitting surfaces thereon.

6. A color picture tube according to claim 1, in which said control grid means includes individual grid members each having a respective one of said apertures therein.

7. A color picture tube according to claim 6, in which said cathode means includes a unitary cathode member having all of said emitting surfaces thereon. 

1. In a color picture tube having a screen with different color phosphors thereon in a repetitious pattern to be made luminescent by the impingement thereagainst of respective intensity moldulated electron beams, and in which the phosphors of one color need to be excited by a beam current substantially larger than the beam currents for the other phosphors in order to obtain a good white balance; the combination of means for generating said electron beams including cathode means having emitting surfaces for the respective beams, and control grid means having portions thereof that are substantially equidistant from said emitting surfaces and apertures in said portions aligned with said emitting surfaces for the passage of the respective beams, the one of said apertures for the passage of the beam corresponding to the phosphors of said one color being of substantially larger open area than the other apertures to provide said substantially larger beam current when a corresponding larger video signal voltage is applied between the respective cathode and control grid means, and said one aperture being divided into parts by said grid means so that said larger open area is constituted by the aggregate area of said parts, whereby to provide said larger beam current without a corresponding difference between the respective cutoff voltages for said beams.
 2. A color picture tube according to claim 1, in which said different color phosphors are red, green aNd blue, respectively, and the phosphors of said one color are the green phosphors.
 3. A color picture tube according to claim 2, further comprising a main electron lens means to focus all of said beams on said screen and an auxiliary electron lens means to cause said beams to cross each other at the effective optical center of said main lens means, and in which the emitting surface and grid aperture for the beam corresponding to the green phosphors are located on the optical axis of said auxiliary and main lens means centrally between the emitting surfaces and grid apertures for the other beams so that the latter pass through peripheral portions of said auxiliary lens means and are subject to spherical errors thereby, whereby to ensure that the landing spots of all of said beams on the respective phosphors are substantially of the same area.
 4. A color picture tube according to claim 1, in which said control grid means includes a unitary grid member having all of said apertures therein.
 5. A color picture tube according to claim 4, in which said cathode means includes individual cathode members each having a respective one of said emitting surfaces thereon.
 6. A color picture tube according to claim 1, in which said control grid means includes individual grid members each having a respective one of said apertures therein.
 7. A color picture tube according to claim 6, in which said cathode means includes a unitary cathode member having all of said emitting surfaces thereon. 